Parabatai
by divergentfan4life
Summary: Jem and Will are more than just friends; they're blood brothers. But how did that all go down? Please read and review!


**Jem and Will have the best, cutest bromance going on, and as soon as I started writing this, I fell in love with the two of them all over again. Hope you enjoy reading as much as I enjoyed writing! Also please review lots and lots!**

Sweat splattered the floor of the training room as thirteen year old William Herondale shook his head in disgust, looking with contempt at the katana that he had just thrown at a target. The blade was lodged in the outermost circle of the bullseye, taunting him.

"Not bad."

Will nearly jumped out of his skin as he cursed in Welsh, his second katana slipping through his hand, leaving a bloody slice.

His best friend had managed to slip into the room almost without a sound, and he now sat right behind Will on the high table off next to the rack of sword from which Will was drawing His silver-streaked eyes sparkled with amusement. "You seem to still be suffering from the terminal illness of poor marksmanship, however."

Will smirking back at Jem in spite of himself as he withdrew his stele and scrawled a hasty _izrate_ over the cut on his hand. "It seems I've been a poor influence on you, James. You've found your sarcasm at last."

Jem quirked a pale eyebrow. "Unfortunately, I don't think my positive influence has been good enough. Despite the hours of my patient instruction, your release on the sword is still ghastly." He slid from the table, cradling the blade of the katana carefully between his fingers. "Watch."

Obediently, Will stepped back as his friend stepped up to the indent in wood floor.

Jem squared his shoulders toward his target, brought the knife behind his head, and, in one smooth exhale, let the blade fly, his wrist snapping forward to follow his line of trajectory. Unsurprisingly, the sword stuck in the center of the target with a decisive thud.

A self-satisfied smile playing across his lips, Jem stepped back, motioning for Will to take his place. "You try."

Releasing an exhale through his clenched teeth, Will tried to mirror his friend's motions. He threw the katana forward as hard as he could, knowing as soon as the blade left his hand that his release was all wrong. Sure enough, the sword didn't even stick, instead clattered to the floor.

Will turned to face Jem, his face twisting in distaste.

His friend looked back at him, a frank smile on his face. "Want to try again?"

"No," Will huffed. "I thought, since I'm already superior to the lot of you with throwing knives, I would try to throw a sword. But I've been practicing for hours, James, do you hear me? Hours!" Will flung his hands into the air, displacing the rack of katanas as he did so.

Jem laughed.

"I was about to cease throwing the bloody objects in favor of slitting the throats of the resident ducks of Hyde Park," Will continued, shooting Jem a playful glare. "So, no, James, to answer your question, I would appreciate very much to not throw katanas any longer."

Jem shrugged. "You're never going to improve that throw of yours if you never practice."

Will, who would have usually turned a comment such as this into a playful fistfight, didn't seem to hear. He stared at his friend intently, as if noticing something for the first time. "Blast practicing," he said finally. "What's the fun in that?" His eyes scanned the rows of weapons lazily, landing on the first blade he saw. "Longswords."

A surprised grin crossed Jem's face. "Dear God," he said, staring at his friend. "Will Herondale, asking me to a longsword duel? I never imagined this day would happen. You know I will win."

Will matched Jem's grin, taking two swords from the rack on the wall and tossing one to his friend. "We'll see."

Jem's eyebrows shot up on his face. "You actually entertain whims of beating me with my favorite weapon?"

Will looked up from the gauntlets he was strapping to his forearms. "Let us raise the stakes then, shall we? If you beat me, I will–"

"Pet a duck," Jem interjected, grinning.

To Jem's surprise, Will didn't object. Fighting back a grimace, he continued, "Very well. But if I should win, you must swear on the angel's name to become my _parabatai_."

Jem looked shocked, then horrified. He whitened, shaking his head. "No, William, I can't…I can't burden you like that…of all people, you are the last one I want to hurt like that."

Will's hands tightened on the hilt of his weapon. His eyes were locked intently on Jem's face. "Why not?"

"I am dying, Will." Jem said it plainly, without any inflection, but Will could read the gravity in his friend's eyes. "I will not allow you to shackle yourself to a dying man. The _Codex_ says that the purpose of _parabatai_ is to create a pair of warriors who protect each other and rely on each other for strength. I'm hardly able to keep myself alive in a fight, William. You need someone stronger."

Will let out a short, humorless laugh. "Stronger? Damn it, James, you're the strongest person I know. You've suffered so much, much more than anyone should have to suffer in one lifetime, but you haven't allowed it to define you. You fight, you train, and you live like any other Shadowhunter, although God knows you deserve to take an easy way out, if you want one." Will stepped closer, gripping his friend's forearm. "You are not a dying addict to me, James Carstairs. You are my friend."

Jem looked sobered, his silvery eyes hardening in resolution against glassy tears. "And I, you, William Herondale," he whispered, looking straight at his friend. "It is a deal, then. If I win, you will pet a duck. And if you win," Jem broke off with a sigh and gave his friend a defeated smile, "I…I _will_ swear on Raziel's name to become your _parabatai._ "

Will almost let relief wash over him, but he quickly hardened his resolution. For once, he let his silky black hair fall into his eyes as he and his friend moved to the center of the training room. "Well then," he said, letting a smirk cross his lips, "you'd better start memorizing the _parabatai_ oath as soon as we're finished here."

Jem grinned at him. "Oh, really that confident in your skills with a longsword, are you?" He lunged for Will, slashing his sword in a downward arch, flipping himself over Will's head against the force of the collision. Metal rang against metal as the two blades crashed together with a violent impact. "I can't remember your skills being anything better than–"

Will didn't let him finish. Before Jem had regained his footing, Will was already charging at him. He parried Jem's blade away, and, twisting underneath the locked swords, flicked his wrist, sending Jem's sword clattering to the floor. Will pressed the edge of his blade to the throat of his friend, grinning at the shocked expression on his face before releasing him.

For a second, Jem just stared at Will, one hand pressed to his throat, looking with disbelief from Will to the sword that his friend still held. Then realization crossed his face, and he smiled ruefully. "If you had told me you'd been practicing with longswords, I would have never agreed, you know."

"Ah, but you did agree, James!" Will said triumphantly. "You agreed to be my _parabatai_ , and so shall you be." He picked up Jem's fallen longsword and handed it to him.

Jem took it, smiling in spite of himself. "So I did."

Will raised his eyebrows at him expectantly. "So," he prompted. "I, James Carstairs…"

Jem sighed and rolled his eyes. "I, James Carstairs, do solemnly swear on Raziel's name to accept William Herondale as my _parabatai._ " He raised his eyebrows at Will. "Satisfied now?"

Will grinned, clapping his best friend, no, his _parabatai_ , on the shoulder. "It will suffice."

The two boys walked out of the training room.

The Institute was empty; both Charlotte and her fiancé Henry were at the Clave meeting, as was Charlotte's father. It was the maid's day off, and Jessamine had sequestered herself in her room, claiming that she needed to 'perfect the ladylike arts'.

So the halls seemed bigger than usual, and more cavernous without the usual noises of life in the Institute as Will and Jem strolled throughout the building.

They were silent, enjoying the companionable silence.

"Why do you want me as your _parabatai_ , Will?" Jem asked suddenly. "I mean, you're my best friend, and I appreciate the touching gesture, but I don't understand. You should have picked someone who can be with you your whole life."

"I love you like my own brother, James, as if you were of my own flesh and my own blood." Will stated it as if it was nothing, but Jem could hear the emotion in his words. "You are the only person who has seen the good that I struggle to find in myself. You take me as I am, and you do not question me. I trust you, Jem; I don't trust anyone."

"Thank you, Will." Jem's voice was quiet; subdued. "And I will be my best self for your sake; I only fear for you when I die."

"You're not going to die."

Jem smiled sadly. "It's inevitable, William. I have a few more months; a year, if I am lucky."

Will ground his jaw. "I'm not going to let you die." The words were harsh, almost pained. "There is a cure, and I'm going to find it, I swear it."

"Will, look at me."

Will locked his eyes on Jem's. "I'm not going to let you die without at least searching."

"Will, the Silent Brothers have already searched everywhere: Downworld, Idris, the City of Bones; nothing. There is nothing to find Will." Jem said it plainly, but Will could see the pain in his eyes. "Please stop looking. I want my last days to be here with you, with everyone at the Institute. I don't want to die when you're on some pointless goose chase that will yield nothing."

Will was silent, his eyes averted.

"Swear it to me, Will. I need to hear you swear it."

"I…I swear." Will looked up at Jem with glassy eyes. "But I will not give up hope."

"Thank you." Jem looked relieved. "I will allow you to hope, but I implore you, please reconsider your offer of _parabatai._ You need someone better, Will, like…"

"Gabriel Lightwood?" Will interjected, looking horrified. "Jessamine?" He laughed, wiping the tears from his eyes as he shoved his friend good-naturedly. "I would rather be your _parabatai_ and have you die a thousand times than be bound by oath to a worm like Gabriel Lightwood, let alone Jessamine."

Jem tried to conceal a smile, to no avail. "Oh, very well. I must concede to Gabriel, though. He brought up a very good point during our discussion of my health the other day. I–"

Will's amused expression turned dangerously protective in a heartbeat. "Jem, if he said one thing against you, I swear to God I'll go break his other arm to teach him a lesson."

"Well, you have my consent, but try to avoid making a scene at the next Christmas party if you can." Jem grinned. "Anyway, he proceeded to tell me that Herondales were as stubborn as rocks."

"Only on certain points," Will amended, looking unrepentant. "Such as the demonic nature of ducks, the irrefutable existence of demon pox, and how Gabriel Lightwood was most certainly a worm in his former life."

Jem laughed. "And on the topics of _parabatai_ , literature, and knife throwing."

"There's that too," Will agreed. "But might I remind you of one thing, James Carstairs: although we Herondales might be extremely stubborn, we are always, always right."

A snort of laughter burst out of Jem. "Remind me of one instance."

"You," Will said, pointing at Jem decisively, "are going to be _my_ parabatai, whether you want to or not. And that, my friend, is the only matter about which being my right is important."

Jem shook his head, still smiling. "Whatever you say, William. Whatever you say."

 **I hope y'all liked it! It was definitely very fun to write and I would love it if you could review/follow/favorite below! It means a lot! xoxo**


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